On Sep 16, 2011, at 10:52 AM, Mark S. Miller wrote:
> On Fri, Sep 16, 2011 at 10:41 AM, Allen Wirfs-Brock <al...@wirfs-brock.com>
> wrote:
> [...]
> This is the exact situation that exists for any ECMAScript dynamic
> allocation. There are no guarantees in the ES spec. that resources allocated
> with an inaccessible object will be freed in a timely manner or ever. Given
> the state of the art of memory management isn't clear how you could make such
> guarantees without unreasonably limiting implementors.
>
> Does everyone, on both sides of this debate, agree that the WeakMap GC issue
> is and the tail-call issue are equivalent specification problems?
>
> I propose that the way to look at both of these is a way I have seen proposed
> somewhere[1] about how to deal with specifying tail calls. Rather than taking
> it as a correctness criteria on an implementation, instead view it as a
> statement about how to analyze the space complexity of programs. When writing
> Andreas' server, it would be nice if he could analyze whether his algorithms
> have O(1) asymptotic space complexity. Does this mean it will succeed on
> every implementation? Of course not. It may be that a given implementation
> doesn't even have enough memory for the server to load. Or the server might
> crash for other reasons.
>
> In order to do this analysis, we need a model of how much memory is retained
> by a computational state -- not in terms of how many bytes, but in terms
> adequate to make statements about asymptotic space complexity.
>
> Then an implementation that runs out of space on programs held to be
> "reasonable" by such analysis can be viewed as low quality implementations.
This all sounds reasonable but I don't see how it particularly impacts the
actual specification.
Allen
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